A wide variety of encoders have been employed and/or disclosed in the past. For example, U.S. Pat. No. 7,714,272 discloses an optical absolute rotary encoder for determining the absolute values of rotational positions with high accuracy. The encoder can include an optical scale having an absolute pattern representing a code corresponding to a single absolute value using a transmitting area and/or an intercepting area. A light emitting unit can be arranged at one side with respect to the optical scale, and configured to project light on the optical scale. A light receiving unit can be arranged at the same side as the light emitting unit, and can be configured to receive light passing through the transmitting area of the optical scale. A light guide unit can be provided and configured to guide the light from the light emitting unit to the light receiving unit. The optical scale and the light emitting unit can rotate relative to each other about an axis of rotation, and the light receiving unit can be disposed on the axis of rotation.
As another example, U.S. Pat. No. 9,121,694 discloses an absolute position-measuring device that includes a first subassembly having a measuring standard on which at least one code track is disposed, and a scanning unit with which, by scanning the at least one code track in a measuring direction, position signals are able to be produced, from which an absolute digital position value is able to be generated. The position-measuring device includes a second subassembly having at least one peripheral unit adapted to perform an additional or auxiliary function of the position-measuring device.
As a further example, U.S. Pat. No. 6,100,822 discloses an optical sensing system which uses a plurality of detectors installed at various positions next to an optical panel to generate a position signal for indicating the position of the optical panel. The optical sensing system has an optical panel having a plurality of sensing areas each having a plurality of encoding holes arranged in a predetermined direction, a sensing device having a plurality of detectors for detecting movements of the optical panel corresponding to the sensing device, each of the detectors being corresponded to one of the sensing areas of the optical panel for detecting movements of the encoding holes along the predetermined direction and generating correspondent sensing signals, and a control circuit electrically connected to the sensing device for collecting the sensing signals generated by the detectors of the sensing device to form a position signal so as to indicate the optical panel's position.